AMMAN, Oct 1 (Reuters) - Alarmed by the rise of al Qaeda in Syria, Saudi Arabia is trying to strengthen rival Islamists with ties to Riyadh and this week helped engineer a consolidation of rebel groups around Damascus under a Saudi-backed leader.

That might bolster the opposition militarily as President Bashar al-Assad's forces have been pushing back, but it also underlines al Qaeda's expansion in Syria - and the proliferation of splits among Assad's enemies, just as world powers are trying to corral them into talks with his government.

Rebel and diplomatic sources said it was Saudi Arabia which nudged rebel brigades operating in and around Damascus to announce this week that they have united under a single command comprising 50 groups and numbering some thousands of fighters.

The formation of the Army of Islam in the capital's eastern fringe under Zahran Alloush, leader of the group Liwa al-Islam, strengthens Salafist jihadis owing allegiance to Riyadh against the Islamic State of Iraq and the Levant (ISIL), an al Qaeda branch which has in recent weeks taken control of territory from other Islamist forces in parts of northern and eastern Syria.

While fighting for religious rule in Syria, local Salafists do not generally share the international ambitions of al Qaeda's jihadists, many of them foreign, who want to drive Westerners from the Middle East and unite Muslims in a single state.

The establishment of the Army of Islam follows last week's joint declaration by groups, mainly in the northeast but also including Liwa al-Islam, who agreed to fight for Islamic rule and also rejected the authority of the Western- and Saudi-backed opposition in exile, the Syrian National Coalition (SNC).

That accord was notably not signed by ISIL.

Zahran Alloush, who founded Liwa al-Islam, or the Brigade of Islam, with his father Abdallah, a Salafist Syrian cleric based in Saudi Arabia, has avoided declaring personal opposition to al Qaeda or to the SNC. But he criticised failures to bring unity to rebel ranks in explaining the creation of the formation:

"We have formed this army ... to achieve unity among the units of the mujahideen and avoid the effects produced by the divisions within the National Coalition," he told Al Jazeera television, referring obliquely to recent rebel in-fighting.

"The Army of Islam is the result of accelerating efforts to unify the fighting units operating in the beloved homeland."

SAUDI CONNECTION

Liwa al-Islam, several thousand strong, is among the biggest and best organised rebel groups, respected even among non-Islamist rebels for integrity and effectiveness. Alloush could not be reached for comment on the Saudi role in his new unit.

Saudi officials do not comment on their operations in Syria, where the Sunni Muslim kingdom has backed the uprising among the Sunni majority against Assad and his minority Alawite elite who are allied to Shi'ite Iran, Riyadh's rival for regional power.

However, rebel and diplomatic sources told Reuters that Saudi Arabia, which furnishes arms and other supplies and funds to Assad's opponents, was behind the Army of Islam.

The commander of an Islamist rebel unit on the opposite side of Damascus from the Army's base of operations in the east told Reuters that Saudi figures had been in touch with various Salafist groups in recent weeks, offering support in return for a common front to keep al Qaeda allies from expanding their presence around the capital - a presence already detected.

"Saudi tribal figures have been making calls on behalf of Saudi intelligence," the commander, who uses the name Abu Mussab, said. "Their strategy is to offer financial backing in return for loyalty and staying away from al Qaeda."

While hoping to avoid outright confrontation with fellow jihadists, the Saudis had been gauging the willingness of local Salafist fighters in joining Saudi-backed formations, including a proposed Syrian National Army. This, Abu Mussab said, might oppose al Qaeda in the way the U.S.-funded Sahwa, or Awakening, movement of Sunni tribesmen fought al Qaeda in Iraq from 2007.

A Western diplomat following the conflict closely said: "Saudi Arabia is growing increasingly uncomfortable with more rebels joining al Qaeda ranks. The recent advances by the Islamic State have embarrassed the Saudis and the new alliance appears designed to stop al Qaeda from gaining influence."

He said Saudi strategy was two tiered: back less extreme Islamist figures in the exile SNC political organisation and woo Salafist brigades on the ground with arms and money.

"Lots of these Salafist groups detest the Syrian National Coalition," he said. "But the Saudis do not see this as a contradiction as long as they stay away from al Qaeda."

Abdulrazzaq Ziad, a liberal activist based in Turkey, said the formation of the Army of Islam, announced with elaborate ceremony in an online video, has already irked al Qaeda: "We are already seeing from Facebook comments of people close to the Islamic State that they view the new formation as a rival."

A second diplomat based in the Middle East said: "We have seen in the last few weeks that every major group has stepped up its efforts to increase its sphere of influence. An alliance like this would not take place without Saudi blessing.

"Liwa al-Islam and its allies have not been comfortable with al Qaeda establishing a foothold in the Ghouta so their interest and that of Saudi Arabia converged," he said, referring to the Damascus suburbs where rebel forces are dug in round the city.

CONFRONTATION

The Salafist movement in Islam, founded on literal readings of early texts, is close to the Wahhabi school associated with the Saudi royal house. Its religious teaching influences al Qaeda but the militant network's Saudi founder, Osama bin Laden, turned against Salafists he saw as allies of a Saudi monarchy that had been corrupted by its alliance with the United States.

The Army of Islam seems to want to avoid fighting al Qaeda for now. After a man named Saeed Jumaa, described as a captain in the Army, told an opposition television station that there could be open conflict with ISIL if they "continue this chaos", Zahran Alloush took to Twitter on Tuesday to disown him.

Jumaa's comments were "dangerous", Alloush said, and were designed to create "strife among Muslims".

The Army of Islam has also avoided an outright break with the SNC: "We do not make enemies of those who are not enemies to us," Army spokesman Islam Alloush told Reuters. However, the group did share the others' criticism of the SNC that it should be directed by fighters inside Syria, not leaders in exile.

If Riyadh's aim is to thwart al Qaeda enemies by rallying local Syrian Islamists in the way Washington did with Iraq's Sunni tribal Sahwa, it may be miscalculating, said commentator Hazem Amin. Unlike the Iraqi fighters, he said, Syrian Salafists were increasingly embracing radical views close to al Qaeda.

"Syria is different," Amin wrote in al-Hayat newspaper. "The social fabric is less cohesive ... At its core, the new Syrian Salafism is jihadist in nature. It is moving towards extremism." (Additional reporting by Alexander Dziadosz; Editing by Dominic Evans and Alastair Macdonald)

We welcome comments that advance the story through relevant opinion, anecdotes, links and data. If you see a comment that you believe is irrelevant or inappropriate, you can flag it to our editors by using the report abuse links. Views expressed in the comments do not represent those of the Thomson Reuters Foundation. For more information see our Acceptable Use Policy.